Preparation, characterization and thermal properties of fatty acid eutectics/bentonite/expanded graphite composites as novel form stable thermal energy storage materials

In this work, bentonite based composite phase change materials (CPCMs) were fabricated by the impregnation of fatty acid eutectics into bentonite clay. In the composites, the pahnitic acid (PA)-stearic acid (SA) eutectics mixtures were undertook as phase change materials (PCMs) for thermal energy storage, and the bentonite were performed as the supporting material. Expanded graphite (EG) was employed for helping restrain the eutectic mixtures from leakage as well as improving thermal conductivity of the CPCMs. The differential scanning calorimetry (DSC) was adopted to assess the thermal properties of the composites, the results showed that the CPCMs have suitable melting temperature of around 54 degrees C with latent heat capacity of 89.12-163.72 kJ/kg. Fourier transformation infrared (FT-IR) and X-ray diffractometer (XRD) were utilized to test the chemical structure and crystalline phase of the CPCMs. The scanning electron microscope (SEM) images revealed that the organic PCMs homogenously spread to the surface and interior of the bentonite. The thermal gravimetric analyzer (TGA) detected that the CPCMs were provided with good thermal stability. As the content of the EG increased, the leakage of the PA SA eutectics reduced considerably. The results from the thermal conductivity meter (TCM) showed that the thermal conductivity of the CPCM with content of 5% EG reached to 1.51 W/(m K) in liquid state and 1.66 W/(m K) in solid state, which was nearly 5.6 times and 4.9 times higher than that of the CPCM without the EG. Experiments displayed that the thermal storage and release rates were noticeably enhanced by combining the EG into original CPCMs. The CPCMs maintained thermal properties after 50 heating cooling cycling. It is envisioned that the satisfactory CPCMs maintain considerable prospects in thermal energy storage.